From Hard Drop - Tetris Wiki

The Nintendo Rotation System, or NRS, is a rotation system divided by two variants. The right-handed version was used in Nintendo's NES Tetris game and Tetris & Dr. Mario.
Tetrominoes spawn with their highest block on row 20.

Right-handed version

Left-handed version was used in Tetris (Game Boy).
Tetrominoes enter with their highest block on row 17.